The development of selective oxidation catalysts for the conversion of methane to methanol or formaldehyde

Abstract

The selective oxidation of methane to methanol and formaldehyde over a series of supported molybdenum and vanadium catalysts has been investigated for a wide range of experimental conditions. Silica supported molybdenum catalysts are suitable for the transformation of methane to formaldehyde at ambient and at elevated pressures in the temperature range 500-600 C, but improved performance in terms of conversion of methane and selectivity to formaldehyde can be achieved by doping the catalysts with small amounts of sodium, copper or iron. Formaldehyde is the only selective oxidation product observed at ambient pressure, but a mixture of this product and methanol forms at pressures of five bar and above. At ambient pressure, conversion of methane increases as the methane partial pressure is decreased but selectivity to formaldehyde is not affected. At higher pressures selectivity to methanol and formaldehyde is less but the total amount of methane consumed is greater. The performances of catalysts which show diminishing selectivity to methanol and/or formaldehyde for increasing methane consumption are compared at ambient and at elevated pressures. An infra-red spectroscopic investigation of supported molybdenum catalysts revealed the presence of methoxy and oxymethylene species on the catalyst surface, following exposure to methane in typical reaction conditions.